1. Field of the Invention
This invention relates to semi-active laser (SAL) designation of targets.
2. Description of the Related Art
The military uses SAL designation to designate targets and guide the missile (weapon) to the target. In SAL designation the designator and the receiver are located on separate platforms. In many battlefield scenarios, SAL designation that maintains “man-in-the-loop” capability is preferred to active designation systems that require the weapon to designate the target. The SAL designator may be man-portable or carried by a designator aircraft such as an unmanned aerial vehicle (UAV).
The operator coordinates via radio with a command center and fires the SAL designator to transmit a narrow pulsed laser beam to place and hold a spot on the target. As soon as the weapon is in range, the SAL receiver starts processing the detected returns to detect the spot, acquire the designated target and to verify that the SAL designator was the source. On a battlefield there can be many ‘false’ returns either randomly generated or generated by enemy countermeasures attempting to jam the SAL receiver. To reduce the ambiguity of designator verification to an acceptable level, the pulses are transmitted at a precise frequency known to the receiver. The receiver performs a time correlation of the known pulse tuned to the known frequency against the detected returns until the target is designated and the designator verified as the source. The SAL receiver also includes processing equipment for generating guidance commands from the pulse-stream to guide the weapon to impact. To support the bandwidth or update requirements of the guidance system, the target must be lased until impact and the frequency of pulses must be high.
The effectiveness of these systems is limited by the need to hold the laser spot on target from initiation through acquisition until impact, and by the potential for systems that can detect the incoming laser and deploy counter measures. The exposure of laser operators or laser platforms increases the length of time that they remain exposed. Also, the power requirements for lasers to generate high-power high-frequency pulses for extended periods to hold a spot on the target can be inhibiting.